Referring to FIG. 1, a gas turbine engine is generally indicated at 10 and comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high pressure compressor 14, a combustor 15, a turbine arrangement comprising a high pressure turbine 16, an intermediate pressure turbine 17 and a low pressure turbine 18, and an exhaust nozzle 19.
The gas turbine engine 10 operates in a conventional manner so that air entering the intake 11 is accelerated by the fan 12 which produce two air flows: a first air flow into the intermediate pressure compressor 13 and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.
The compressed air exhausted from the high pressure compressor 14 is directed into the combustor 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines 16, 17 and 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low pressure turbines 16, 17 and 18 respectively drive the high and intermediate pressure compressors 14 and 13 and the fan 12 by suitable interconnecting shafts.
In view of the above it will be appreciated that control of flows through a gas turbine engine are important to achieve efficiency and operational performance. In such circumstances in order to extract propulsion and work blades secured upon rotor hubs are associated with stators to cause appropriate directionality with respect to flows through an engine. It will also be appreciated that the loads presented to the engine may vary over operational cycles such as takeoff, cruise, ascent, descent and landing if the engine is utilised for aircraft propulsion. It is found that highly loaded rotors and stators stall about the hub/shroud area due to secondary flows sweeping low momentum fluid from the annulus about the rotor hub and stator shroud onto the stator blades near to the peak suction point on the suction surface of the blades. In such circumstances subsequent operation is less efficient and effective over those blade suction surfaces. It would be advantageous to reduce or inhibit the effects of such secondary flows to improve engine efficiency and performance.
It will be appreciated that secondary flows relate to fluid flows through the engine blades near to the hub or shroud surface which are not part of or of lower momentum than the primary propulsion flows.